Voltage divider



March 3, 1959 R. o. HELD 2,876,319

VOLTAGE DIVIDER Filed Sept. 28, 1956 2 Sheets-Sheet 1 I y I) iiINVENTOR. 2055270. #540 United States Patent VOLTAGE DIVIDER Robert 0.Held, Los Angeles, Calif. Application September 28, 1956, Serial No;612,701 7 Claims. (Cl. 201-43 This invention relates to voltagedividers, and more particularly to a voltage divider of animprovedmechanical and electrical construction.

Although many features of the.invention may be employed in voltagedividers of any size, the invention is particularly useful insub-miniature voltage dividers, or more commonly potentiometers, for usein large quantities in printed, painted or etched circuits.

Several pressing problems currently exist in the art of makingsub-miniature potentiometers. One of the most important problems relatesto their automatic and economical fabrication and installation. To thepresent time, potentiometer construction has not kept' pace withautomatic machinery and assembly methods, Hence, sub-miniaturepotentiomete'rs cost very little, if any, less than otentiometers ofaverage size.

Another problem relates to the construction of subminiaturepotentiometers having good and low noise wiper contacts.

A third problem relates to the difliculties encountered in' mounting apotentiometer on a perforated printed circuit board. For example, it isat present the practice to use screws or other means to mount them,although all other elements are provided with simple wire leads, all theelements having their leads projecting through metal walled apertures ina single board in which they are soldered by dipping all the leadssimultaneously in melted solder.

The invention overcomes these and other disadvantages of the prior artby providing several construction features which permit automaticmanufacture and installation of voltage dividers.

The first of these features comprises a cap assembly to support a wiperin a rotatable position. This cap assembly comprises a housing coverhaving a cylindrical aperture therein, resilient means to urge the bodyout of the aperture, and means to maintain the body in a fixed axial,but rotatable angular position through the aperture to stress theresilient means. Preferably, the resilient means comprises an O-ringlocated around the shaft between the flange and the housing cover. Thehousing cover may be constructed to snap tight over a housing body sothat it may be easily assembled. The O-ring serves two purposes. In thefirst place, it keeps the voltage divider housing liquid tight.Secondly, it serves as friction drag means to resist rotation of theshaft.

According to a specific feature of the invention, means for maintainingthe shaft in a fixed axial, but rotatable angular position includes aretaining pin to project through a transverse hole in the shaft belowthe housing cover provided for that purpose. The shaft is thus easilyfixed in position in the housing cover simply by inserting the retainingpin through it. The resilient character of the 0-ring may serve to keepthe pin in place. Preferably a washer is located around the shaftbetween the pin and the housing, and the pin is made of a coiled stripof the spring steel material. This construction may pro- 2,876,319Patented Mar. 3, 1959 ice vide an additional force to maintain the pinin a fixed transverse position.

In accordance with one aspect of the invention, a stop may be moldedintegrally with the housing cover and engage the pin to limit therotation of the shaft, provided that the pin is placed in a suitabletransverse position. This arrangement has an additional advantagein thatif the pin is sufficiently short, it may be adjusted either to avoid orto engage this stop. This means that the same component parts of thepotentiometer may be employed to meet either one of these twospecifications, viz. (1) that stop means must'be provided or (2) thatstop means must be omitted.

Another sub-assembly of the potentiometer of the invention which may beeasily and quickly assembledineludes an arrangement for fixing a wiperassembly on the shaft. This arrangement comprises a wiper shaft having acircumferential groove therein, an annular insulator disposed about theshaft in the groove, the insulator being sutficiently resilient to passover the length of the shaft included between one end and the groove,and a member having an annular opening through it to fit around theinsulator, the opening being sufficiently small indiameter to maintainthe insulator in radial compression.

According-to another aspect of the invention, a potentiometer isprovided comprising a housing. having a radial projection to act as: aguide for a machine installation thereof in mounting the potentiometeron a printed or etched circuit board.

According to still another feature of the invention, a potentiometer isprovided comprising a housing having a mark thereon at least on one endthereof to identify the physical position of the structure internally ofthe housing. In a particular use of such a potentiometer, the mark maybe employed on the top of the potentiometer housing to identify theangular position at which the wiper lead emanates from the bottom of thehousing. All the potentiometer leads emanating from the bottom of thehousing may then be easily manually inserted in holes in a printedcircuit board.

Good wiper contact is provided in accordance with the invention byanother arrangement for use in a potentiometer having a housingincluding a cover and a shaft extending therethrough in a fixed axial,but rotatable angular position, a stationary element in a fixed positionin said housing providing a contacting surface below the inner end ofthe shaft, and a winding having a wiping surface disposed concentricallywith the shaft. The arrangement then includes a conductive discinsulated from but fixed to the shaft internally of the housing in aplane substantially perpendicular to the axis of the shaft, the dischaving an upper surface adjacent the housing cover and an opposite lowersurface, resilient means fixed to the disc at a point on its peripheryand extending downwardly therefrom, and means fixed to the resilientmeans to contact the stationary element, the resilient means urging saiddisc upwardly at the one point, and a wiper having one end fixed to thedisc at another point on the periphery thereof diametrically opposed tothat of the one point and contacting the wiping surface of the winding,whereby the action of the resilient means forces the contact meansagainst the stationary contact element, and the wiper against the wipingsurface of the winding.

A bifurcated wiper contact, which is employed in the potentiometer ofthe invention, minimizes noise. In fact, the noise figure ofconventional contacts may be reduced as much as 20% by utilizing thebifurcated wiper contact.

Leads to the wiper and potentiometer winding are molded integrally withthe housing in accordance with another feature of the invention, wherebythe leads may be easily soldered to a printed circuit board.

In accordance with another related feature of the invention, a portionof the length of each lead has an irregular cross-section to preventeach of them from slipping outwardly of the housing.

It is therefore an object of the invention to provide a voltage dividerhaving a plurality of component parts which may be fabricated, assembledand installed automatically.

It is another object of the invention to provide a voltage dividerincluding means to provide good and low noise wiper contacts.

It is still another object of the invention to provide a voltage dividerhaving wire leads with a strong attachment construction to a housingtherefor to permit the leads to be soldered to a printed, painted oretched circuit board in a most efficient manner.

These and other objects and advantages of the invention will be betterunderstood when considered with the following description taken inconnection with the accompanying drawings made a part of thisspecification, wherein several embodiments are illustrated by way ofexample. The device of the present invention is by no means limited tothe specific embodiments illustrated in the drawings since they areshown merely for purposes of description.

Fig. l is a plan view of one embodiment of the voltage divider of theinvention;

Fig. 2 is a front elevational view of the voltage divider shown in Fig.1;

Fig. 3 is a bottom view of the voltage divider;

Fig. 4 is an enlarged sectional view of the potentiometer taken on theline 4-4 shown in Fig. 1;

Fig. 5 is a broken away enlarged sectional view of the voltage divider;V

Fig. 6 is a sectional view of a retaining pin taken on the line 66 shownin Fig. 4;

Fig. 7 is an enlarged broken away sectional view of a wiper shaftassembly shown in Fig. 4; and

Fig. 8 is a bottom view of the wiper shaft assembly taken on the line8-8 shown in Fig. 4.

In the drawing in Fig. l a voltage divider is shown including a housing10 having a key projection 12 extend ing longitudinally of and at apoint on the periphery of the housing 10. The key projection 12 may beemployed to guide the housing 10 in an automatic installing operation ofthe voltage divider on a printed or etched circuit board. The voltagedivider also includes a wiper shaft 14 having a slot 15 which isemployed to carry a wiper, not shown, in Fig. 1, the wiper beingconnected to a lead emanating from the bottom surface of the housing 10and indicated in a dotted circle 16. Two other leads 18 and 20 alsoemanate from the bottom surface of the housing 10 and are connectedinternally of the housing 10 to opposite ends of a winding, which is notshown in Fig. 1.

A colored dot 22 is disposed adjacent the position of lead 16 toidentify its position so that when the leads extend in substantiallyparallel directions from the bottom surface of the housing and, as shownin Fig. 2, the voltage divider may be easily mounted on a printedcircuit board.

The housing 10 includes a body portion 24 and a cover 25 including anupwardly extending short hollow cylindrical projection 26. Theprojection 26 is employed to house an O-ring, not shown in Figs. 1 and2, but which is shown in detail in Fig. 4. The projection 26 need notnecessarily be employed although it may serve to keep the voltagedivider liquid tight in that it cooperates with the O-ring to provide abetter liquid tight seal around the shaft 14 and between the shaft 14and the housing 10.

Fig. 3 is a bottom view of the housing 10 including the key projection12, wiper lead 16, and winding leads 18 and 20. A colored spot 28 isalso provided on the bottom surface of the housing 10 as shown in Fig. 3to identify the wiper lead 16. It may be desirable to identify someother structure internally of the housing 10. According to the inventioneither of the spots 22 or 28 may be used for this purpose.

In Fig. 4, it is to be noted that shaft 14 is provided with an outwardlyextending radial flange 30 to engage the upper surface of projection 26and also to overlie an O-ring 32 which is compressed between the flange30 and the housing cover 25. The O-ring 32 tends to urge the shaft 14outwardly of the cover 25. This force is resisted by a retaining pin 34that extends through a transverse cylindrical passageway 36 through theshaft 14. A washer 38 is preferably disposed about the shaft 14 betweenthe housing cover 25 and the pin 34 to facilitate movement of the pin 34relative to the housing cover 25.

By the use of this structure the voltage divider may be maintainedliquid tight. In addition, the O-ring 32 may serve to resist movement ofthe shaft 14 so that vibration will not cause the position of a wipercontact indicated at 40 to move over a wiper surface 42 of a resistivewinding indicated at 44.

The function of pin 34 in one instance is simply to provide means toresist the axial force on shaft 14 provided by O-ring 32. Anotherfunction is to provide stop means; this stop means including adownwardly directed projection 46 which may be made integrally withhousing cover 25. As stated previously, the transverse position of pin34 may be adjusted to either engage or to avoid projection 46 where, byusing the same parts, the voltage divider may be constructed to meet twospecifications, i. e. to either provide stop means for the shaft 14, ornot to provide a stop means for the shaft 14.

Body portion 24 of housing 10 is preferably constructed of a plastic andtherefore somewhat resilient material. If the upper end of the bodyportion 24 is provided with a groove as indicated at 45 in Fig. 5, thecover 25 may be snapped into position in the groove 48. Preferably aspace 50 is left between the cover 25 and the body portion 24, whereby asealing fluid may be deposited between them to insure a liquid tightseal for the voltage divider.

In Fig. 6 a cross-section of the pin 34 is shown. The pin may have aspiral cross-section and be made of spring steel. The expansion force ofthe spring will thus maintain the pin 34 in a substantially fixedposition in the passageway 36 of shaft 14. This means that the pin 34need not be provided with an additional retaining means.

In Fig. 7 a lower portion or axial projection 52 of the shaft 14 isshown in an enlarged sectional view. The projection 52 is preferablytapered as shown providing substantially a groove at a point along thelength of the shaft indicated at 53. An annular body 54 which may bemade of a resilient material is then slip fit over the projection 52.After the body 54 is then slipped in position on the projection 52, aconductive disc is slip fit over the body 54 to maintain it in radialcompression. The disc may serve to support the bifurcated wiper 49 towhich it is connected by two spot welds 58 as shown in Fig. 8. Wiper 44)is bifurcated as indicated at a slot 60 which may betwo mills inthickness. A leaf spring 62 which is fixed to the opposite side of thedisc 56 by means of spot welds 64 has a dual function. In the firstplace it causes the wiper 46 to positively engage the wiping surface 42of winding 44, and in addition it, itself, positively engages astationary element or wiping contact 66 shown in Fig. 4. The leaf spring62 is made of a con ductive material and therefore directly connectsWiper 40 to element 66. Element 66 is in turn electrically connected tothe inner end of wiper lead 16. The fact that disc 56 maintains body 54in radial compression makes it impossible for body 56 to slip off ofbody 54 from the effects of vibration or shock. I11 addition, leafspring with wiper 40 tends to keep the disc 56 in a stable mechanicalposition about the body 54.

The inner ends of leads 13 are connected to opposite ends of winding 44which is preferably wound simply on a dielectric card, the card beingdisposed in a cylindrical card-shaped form 68 inside the body portion 24of housing 10.

It is to be noted that body portion 24 of housing includes a centralportion 71 which extends upwardly toward cap 25. The leads 16, 18 andare thus molded integrally with this extension. Leads 16 and 18 arepreferably provided with irregular cross-section through an intermediatelength extending through the extension 71. These irregularcross-sections are indicated at 70 and 72 respectively. Lead 20 also isprovided with a similar irregular cross-section in its intermediateportion in the extension 71, although this is not shown. By the use ofthis arrangement the voltage divider may be mounted directly from theleads 16, 18 and 20, they serving as structural supports as well as leadin wires.

It will therefore be seen that the manufacture and assembly of thevoltage divider shown in Fig. 4 may be made with a minimum amount oftime and expenditure of labor, and a minimum number of inexpensivecomponent parts. For example, the housing cover may be easily fabricatedfroma plastic material. The leads 16, 18 and 20 may be bought simply aswires in commercial quantity and may subsequently be mashed irregularlyon their intermediate portions as at 70 and 72. Leads 16, 18 and 20 arethen supported in a mold suitable for making the body portion 24 ofhousing 10 and the plastic material employed in the body portion 24 maythen be poured to mold the leads 16, 18 and 20 therewith. After this isaccomplished, stationary element 66 may be bonded to the top of theextension 71 by means of glue or other convenient means. Preferably itis provided with an aperture at 74 through which wiper lead 16 mayextend. The wiper lead may then be peened over to make good electricalcontact with element 66. Resistive winding 44 may be easily wound on theflexible card 68 in a conventional manner. The card is then inserted inthe body portion 24 and preferably the ends of the winding 44 are spotwelded to the inner portions of winding leads 18 and 20.

At this stage of the manufacture the body portion 24 is immediatelyready to be assembled with the cover 25 of the housing. All theremaining elements in the voltage divider are then fixed to the cover25. This assembly may be performed in a convenient manner. All thecomponent parts of the cover assembly including the cover 25 may bestamped except shaft 14 which must be turned on a lathe and pin 34 whichmust be specially made. O-ring 32 and resilient body 54 may be easilybought on the open commercial market. If the configuration of body 54cannot be purchased, it can obviously be easily fabricated. Wiper 40 ispreferably bifurcated by two mill grinding wheel which is often employedin watch making. Wiper 40 and leaf spring 62 are then spot welded todisc 56. O-ring 32 is then mounted beneath the radial projection offlange of shaft 14 and the shaft 14 is inserted into an aperture 76 inthe cover 25 pro vided therefor. Washer 38 is then placed over theshaft, and pin 34 is pushed through passageway 36. Body 54 is then pressfit over the axial projection 52 of shaft 14 and disc 56 is press fitover the body 54, wiper 40 and leaf spring 62 having been spot welded ina sub-assembly step. Cap or cover 25 of housing 10 is then snap fit intothe groove 48 as illustrated in Fig. 5 and the voltage divider iscompletely assembled.

Although one specfic embodiment of the invention has been shown anddescribed, it will be obvious to those skilled in the art that otherchanges and modifications may be made therein without departing from thetrue 6 scope of the invention as defined in the appended claims.

What is claimed is:

1. In a voltage divider, a cap assembly to support a wiper in arotatable position, said cap assembly comprising: a housing cover havinga cylindrical aperture therein, a rotatable body to project through saidaperture,

said body having an outer radial flange larger in diam? eter than saidaperture, a resilient O-ring located around said body between saidflange and said housing cover on one side of said housing cover, andmeans for connection with said body on the other side of said housingcover to maintain said body in a fixed axial, but rotatable, angularposition through said aperture to compress an O-ring between said flangeand said housing cover for expeditious assembly thereof and forproviding a fluid tight seal between said body and said housing cover.

2. The invention defined in claim 1, wherein said body is provided witha transverse hole below said housing cover and wherein said meansincludes a retaining pin to project through said hole.

3. The invention as defined in claim 2, wherein said pin is made of acoiled strip of a resilient material.

4. The invention as defined in claim 3, wherein said pin is made ofspring steel, and wherein a washer is located around said body betweensaid housing cover and said pin.

5. The invention as defined in claim 2, wherein stop means are providedon said housing cover to engage said pin when it is set in a firsttransverse position to limit the rotational movement of said body, andto avoid said pin when it is set in a second transverse position.

6. In a potentiometer, the combination comprising: a housing cover; awiper shaft having a circumferential groove, said shaft extendingthrough said cover; means to maintain said shaft in a fixed axial, butrotatable angular position; an annular insulator disposed about saidshaft in said groove, said insulator being sufiiciently resilient topass over the length of said shaft included between one end of saidgrooves; and a member having an annular opening through it to fit aroundsaid insulator, said opening being sufficiently small in diameter tomaintain said insulator in radial compression.

7. A voltage divider comprising: a housing including a cover, a shaftextending through said cover in a.fixed axial but rotatable angularposition, a stationary element in a fixed position in said housingproviding a contacting surface directly below the inner end of saidshaft, a winding having a wiping surface disposed concentrically withsaid shaft, a conductive member insulated from but fixed to said shaftinternally of said housing in a plane substantially perpendicular to theaxis of said shaft, a leaf spring having one end fixed to saidconductive member at a point around and spaced from said shaft andanother end spaced from and located directly below the lower end of saidshaft in line with the vertical axis of said shaft to be forced intoelectrical contact with said stationary element at a point directlybelow the lower end of said shaft, and a wiper having one end fixed tosaid conductive member at another point around the periphery of saidshaft diametrically opposed to said one point and contacting the wipingsurface of said winding.

References Cited in the file of this patent UNITED STATES PATENTS Polyeet al. u- Mar. 27, 1956

